This invention relates to a vehicle restraint, and in particular to a mechanical device which is used to restrain a vehicle which has been parked at a loading dock.
Vehicle restraints have been used in the material handling industry to prevent a vehicle from moving away from a loading dock as it is being loaded and/or unloaded. In general, these devices act as substitutes for chains and wheel chocks. They share a common trait in that all use the ICC bar of the vehicle as the technique by which the vehicle is engaged and restrained. Such ICC bars are required by law and are placed at the rear end of the vehicle within specified height and distance parameters from the ground and the rear of the vehicle. As the vehicle is loaded and/or unloaded it tends to "float", that is, move vertically thereby varying the vertical position of the ICC bar from the ground. Various devices have been proposed and some placed into practice to restrain vehicles yet take into account vehicle float. Existing vehicle restraints fall into three general categories.
The first category of vehicle restraints are those which employ a carriage having rollers or the like which ride on tracks mounted to the dock wall. The use of a vertically moving carriage provides range to engage ICC bars at different heights. Representative are U.S. Pat. Nos. 4,472,099, 4,443,150, 4,282,621, 4,264,259 and 4,695,216. In these devices the rollers are subjected to restraining loads and repeated motion as the truck moves up and down while it is being loaded or unloaded. Thus, these restraints are generally high maintenance items given the mechanical arrangement. Additionally, some of these vehicle restraints require impact by the truck to position the device so that it can locate the ICC bar. That is, the vehicle backs into position and the ICC bar strikes the restraint which results in movement of the restraint to position a locking hook relative to the bar. This causes additional shock loads on the track and roller mechanism. Moreover, the track itself must be supported by a building wall and, in the case of a loading dock, may interfere with the operation of the leveler itself. In other cases a wall may not be present or the wall material may be a cinder block or other material not strong enough to support the vehicle restraint.
A second class of devices employ a vertical bar which is raised to a position in front of the ICC bar restraining the forward motion of the vehicle. Various techniques have been proposed to raise such a bar. In U.S. Pat. No. 4,634,334 an electric motor is used to reciprocate a bar from an inoperative position to an operative position. A swinging hook mechanism manually operated is disclosed in U.S. Pat. No. 4,605,353. U.S. Pat. No. 4,784,567 employs a device having a cylinder sunk into the ground with the bar being vertically raised as its slides upward on a track. Thus, as noted, some of these devices pivot the bar into the vertical raised position. In those cases because the bar must fully pivot to the vertical position, the raised height of the bar is constant and may interfere with hitches or other equipment mounted on the underside of the vehicle.
Still, others, such as U.S. Pat. No. 4,784,567, telescope upward from a fixed housing and therefore can be raised to any required height while staying below the equipment on the truck which might interfere. However, any telescoping device has a limitation that the length of the housing must be greater than the travel of the moving part. For example, to reach a height of 30 inches above the ground, maximum height for an ICC bar, one device has a housing height of 17 inches and a travel of 13 inches providing an overlap of 4 inches at maximum extension. However, a high housing prevents use with low trucks some of which are less than 13 inches above the driveway. Other devices used have a housing which is shorter, 12 inches above the driveway with a travel of 18 inches. These, however, require a hole to be excavated in the driveway to allow the bar to retract into the lower part of the housing.
A third class of devices use one or more hooks which pivot about a fixed hinge mounted on the dock wall. The arc of travel of the hook causes the distance from the wall to the hook to vary as it moves up and down. If the distance decreases as the truck is loaded or unloaded the hook can trap the truck so that it will not release when desired. Typical of such devices are U.S. Pat. Nos. 4,208,161 and 4,605,353.
To overcome some of these deficiencies the art has also suggested a series of complex linkage mechanisms to provide both low profile yet sufficient capture range so that a vehicle will be "captured" and restrained. Typical of those vehicle restraints are U.S. Pat. Nos. 4,674,941 and 4,695,216. In those cases given the complex mechanisms which require roller bearings and the like, the vehicle restraints again are high maintenance items. Also, the restraining member itself may not move vertically but rather, have an arcuate movement as the device is erected thereby raising the question of potential interference and blockage as a result of items which project from the bottom of the truck.